There are generally two types of LED loads, i.e., voltage-type LED load and current-type LED load. A voltage-type LED load requires a constant-voltage output from a LED driver, while a current-type LED load requires a constant-current output from the LED driver. In order to meet the requirements of both types of LED loads, a standard power supply with a case (A can) is widely applied in the LED driver market in North America. For example, a 100 W class 2 output of LED power supply is generally rated at 24V/4.1 A. Such LED driver usually has an output of both constant-current and constant-voltage. That is, when the output voltage is smaller than 24V, the power supply works in a constant-current mode at 4.1 A; and when the output voltage reaches 24V, the power supply is maintained at a constant-voltage at 24V.
With increasing demands from energy consumption, it is desirable that a LED driver can have not only the above functions but also a dimming function. Since the current-type LED load and the voltage-type LED load usually require different dimming schemes and circuits, they generally require two specialized driving power supplies respectively. However, using two specialized driving power supplies in a LED driver results in an increased size and a complicated structure of the LED driver. This means an increased cost.